FIG. 6 shows one example of the structure of the organic electroluminescence element. The organic electroluminescence element comprises a light transmissive substrate 6, a light transmissive electrode 1 which is defined as an anode, a hole transport layer 8, a light emission layer 3, an electron transport layer 9, and a light reflective electrode 2 defined as a cathode. The light transmissive electrode 1, the hole transport layer 8, the light emission layer 3, the electron transport layer 9, a light reflective electrode 2 are provided on the upper surface of the light transmissive substrate 6 such that the light transmissive electrode 1, the hole transport layer 8, the light emission layer 3, the electron transport layer 9, a light reflective electrode 2 are arranged in order. In this organic electroluminescence element, when the voltage is applied between the electrode 1 and the electrode 2, the electron is injected into the light emission layer 3 through the electron transport layer 9. Similarly, when the voltage is applied between the electrode 1 and the electrode 2, the hole is injected into the light emission layer through the hole transport layer 8. When the electron is recombined with the hole in the light emission layer 3, the light emission is made in the light emission layer 3. The light emitted in the light emission layer 3 is sent to the outside through the light transmissive electrode 1 and the light transmissive substrate 6.
Such the organic electroluminescence element has a property of emitting the light by itself. In addition, the organic electroluminescence element has a light emission property of comparatively high efficiency. In addition, the organic electroluminescence element has a property of emitting the light having various colors. The organic electroluminescence element is expected to be used for the luminous body for the display device such as flat panel display, a light source such as a backlight of the liquid crystal display, and a lighting device. In addition, a part of the organic electroluminescence element is practically used.
However, the organic electroluminescence element is a thin film device having a thickness which is approximately same as an order of the optical wavelength. In addition, the organic electroluminescence element has the thickness which is correlated with the light emission property. Thus, there is a necessity for the device structure of the electroluminescence element to have the design of the film design which is suitable for both the electrical design and the optical design.
In general, when the organic electroluminescence element generates the light in the light emission layer 3 of the organic electroluminescence, the light is totally reflected by the light emission layer 3, the organic layer 4, inside of the electrode, and the inside of the substrate 6, whereby the light generated in the organic electroluminescence element is confined in the light emission layer 3, the organic layer 4, inside of the electrode, and the inside of the substrate 6. According to a simple estimation, when the light emission layer 3 generates the light, 50 percents of the light generated in the light emission layer 3 is confined in the inside of light emission layer 3, the inside of the organic layer 4, and the inside of the light transparent electrode 1. In addition, 30 percents of the light generated in the light emission layer 3 is confined in the inside of the substrate 6. Therefore, the an amount of the light which is emitted to the outside is only 20 percents of the total amount.
In addition, as shown in FIG. 7, it is well known for the substrate 6 that the light scattering region 7 is disposed on the outer surface of the substrate 6. The light scattering region 7 allows a part of the light confined in the substrate 6 to be extracted to the outside of the organic electroluminescence element. This configuration makes it possible to increase an amount of the light which is extracted to the outside of the organic electroluminescence element.
In addition, as shown in FIG. 1, it is well known to employ the light transmissive electrode 1 and the substrate 6 with a light scattering region 7 between the light transmissive electrode 1 and the substrate 6. In this case, a part of the light which is confined in the light emission layer 3, the organic layer 4, and the light transmissive electrode 1 is extracted from the organic electroluminescence element. As mentioned above, an amount of the light which is confined in the light emission layer 3, the organic layer 4, and the light transmissive electrode 1 is greater than an amount of the light which is confined in the substrate 6. Therefore, the organic electroluminescence element comprises the light transmissive electrode 1 and the substrate 6 with the light scattering region 7 between the light transmissive electrode 1 and the substrate 6 is configured to emit the light having an amount which is greater than an amount of the light which is emitted from the organic electroluminescence element comprising the substrate 6 with the light scattering region 7 on the outer surface of the substrate 6.
In addition, in such the organic electroluminescence element, there are some reports of the organic electroluminescence element having a designing of the distance between the luminous point in the light emission layer 3 and the light transmissive electrode 2 in order to increase an amount of the light which is given off to the outside of the organic electroluminescence element. For example, the organic electroluminescence element disclosed in the patent literature 1 has a luminous point and the light transmissive electrode 1 to create a distance between the luminous point and the light transmissive electrode 1; the distance between the luminous point and the light transmissive electrode 1 is approximately equal to an even multiple of the one-quarter of the wavelength. In addition, the organic electroluminescence element has the luminous point and the light reflective electrode 2 to create a distance which is approximately equal to an odd multiple of one-quarter of the wavelength. The patent literature 2 discloses the electroluminescence element comprising the electrodes which are arranged to create the distance between the electrodes; the distance is determined on the basis of the phase shift of the light. The patent literature 3 disclose the organic electroluminescence element comprising the light transmissive electrode 1 and the light reflective electrode 2 which are arranged to create the distance between the light transmissive electrode 1 and the light reflective electrode; the distance is set within a predetermined range which is determined on the basis of the phase shift of the light in the light reflective electrode 2. In addition, each one of the patent literature 4 and the patent literature 5 discloses the organic electroluminescence element which comprises the substrate 6 with the light scattering region 7, and the electrodes which are arranged to create the distance between the electrodes; the distance between the electrodes are determined to have a predetermined value.
Each one of the patent literatures discloses that the organic electroluminescence element has the luminescence efficiency which is greatly related to the thickness of the light transparent film which constitutes the organic electroluminescence element. In addition, each the patent literature discloses to employ the luminous point and the light reflective electrode 2 with “the film having a particular optical thickness” between the luminous point and the light reflective electrode 2 in order to obtain the good efficiency under a condition where the particular optical thickness satisfies the following exemplified formula. “The particular optical thickness is equal to (2m+1)/4 multiple of the luminous wavelength (m is an integer number and is more than zero).
However, the patent literature 1 fails to disclose the consideration of the phase shift of the light in the light reflective electrode 2. In addition, the patent literature 2 discloses the target spectrum; the half width of the spectrum is limited to be equal to or less than 50 nanometers. The patent literature 3 only defines the distance between the electrodes. In contrast, the patent literature 3 discloses no definition of the distance between the luminous point and the light reflective electrode 2. Furthermore, each one of the patent literatures 1 to 3 discloses the optical designing of the organic electroluminescence element which employs the substrate and other members without light scattering region 7 on the substrate and other members.
In contrast, each one of the patent literatures 4 and 5 discloses the organic electroluminescence element which comprises the light scattering region 7. However, each one of the patent literatures 4 and 5 only disclose only the definition of satisfying the above formula under a condition where the “m” is equal to zero. Therefore, it is impossible to apply the technical feature of the above to the situation where there is a necessity to arrange the light emission layer 3 and the light reflective electrode 2 to create the distance of a certain level between the light emission layer 3 and the light reflective electrode 2. This is similar to the patent literature 2.
In view of this, the applicant of this application discloses the appropriate distance between the luminous point and the light reflective electrode 2 in a case where the light scattering region 7 is disposed on the outer surface of the substrate 6 shown in FIG. 7 and where there is a need to create the distance between the light emission layer 3 and the light reflective electrode 2, with respect to arbitral luminescence spectrum.
However, as will be understood from the previous explanation, the organic electroluminescence element comprising the light scattering region 7 between the light transmissive electrode 3 and the substrate 6 emits the light which has an amount which is greater than an amount of the organic electroluminescence element comprising a light scattering region 7 on the outer surface of the substrate 6. With regard to the organic electroluminescence element having this configuration, a design principle of the suitable distance between the luminous point and the light reflective electrode 2 under a situation where a certain distance is needed between the light emission layer 3 and the light reflective electrode 2 with respect to the arbitral emission spectrum is not cleared.
In addition, recently, an organic electroluminescence element of new type shown in FIG. 2 is disclosed. This organic electroluminescence element comprises a plurality of the light emission layers 3 and a charge supply layer 10 which is disposed between the light emission layers 3; the charge supply layer 10 comprises a light transmissive electrode, and a charge generation layer which comprises layers such as a an organic semiconductor, an inorganic semiconductor, an electron accepting material, and an electron releasing material. A plurality of the light emission layer 3 are stacked along a thickness direction of the organic electroluminescence element. The organic electroluminescence element of the above type has a possibility of emitting the light having a high brightness, and of long operating life, whereby the organic electroluminescence element of the above type is highly expected its future progress. However, the principle of the optical design for the future progress is not clear yet. Furthermore, there is no report of the configuration of providing “a region for reflecting the light and disturbing the angle of the light 7” between the light transmissive electrode 1 and the substrate 6.